Ion source

ABSTRACT

An ion source for use in ion assisted deposition of films, has a ionisation region, a gas supply, supplying ionisable gas to the ionisation region, a gas excitation system causing ionisation of the gas, ion influencing means forming the ions into a current directed at a target, and an ion source controller controlling the ion source so as to intermittently produce the current.

BACKGROUND OF THE INVENTION

[0001] This invention relates to ion sources used in Ion AssistedDeposition (IAD) of films, in particular optical quality films and tomethods of operating such ion sources.

[0002] Ion sources had their origins in space propulsion but morerecently have found use in industrial processes such as IAD of thin filmcoatings. In an LAD process, an ion beam from an ion source is directedtoward a target substrate to cause densification of the coating materialas it is deposited. The process occurs within an evacuated chamber ofpressure of the order 10⁻² Pa or less.

[0003] The benefits that result from ion assistance, during growth, ofalmost any optical material is well understood and is today widelypracticed. In general, ion bombardment provides close to bulk density ofthe film resulting in dramatic improvements in durability andperformance. However, for many classes of materials this benefit isaccompanied by an undesirable modification of optical propertiesobserved as an increasing absorption coefficient (k) and variability inrefractive index (n). For many classes of materials, this problemresults from incompatibility between the ion species and depositingmaterial.

[0004] Argon and oxygen are the two must predominant species of ionsused in LAD processes. The high momentum (of Ar+ provides high packingdensity, although usually leads to a reduction of metal oxides andfluorine depletion of most metal fluorides. This results in metal-richfilms with a subsequent increase in optical absorption.

[0005] The use of O+ is well suited to the IAD of metal oxides such astitania, silica etc. With the correct choice of energy and ion currentdensity, O+IAD can provide fully densified and low-stress films. Problemarise however where the very chemically active oxygen ions displacefluorine atoms from depositing molecules immediately prior to theirincorporation in the film. This leads to the growth of oxy-fluorideswith subsequent deterioration of optical properties. The extent to whichthis occurs depends on factors such as ion energy and current.

SUMMARY OF THE INVENTION

[0006] In a first aspect the invention resides in an ion sourceincluding:

[0007] an ionisation region;

[0008] a gas supply;

[0009] a gas excitation system;

[0010] ion influencing means; and

[0011] an ion source controller;

[0012] wherein said gas supply supplies an ionisable gas to saidionisation region;

[0013] wherein said gas excitation system causes ionisation of gas insaid ionisation region;

[0014] wherein said ion influencing means forms ions produced in saidionisation region into an ion current substantially directed at atarget;

[0015] and wherein said ion source controller controls said ion sourceso as to intermittently produce said ion current.

[0016] In a first embodiment, gas is intermittently introduced into theionisation region.

[0017] In a second embodiment the flow of electrons into the ionisationregion is made intermittent.

[0018] In a further embodiment the ion source of the present inventionis combined with film deposition apparatus, the combined apparatusincluding a deposition control system at prevents deposition of newmaterial onto the target substrate while the ion current is directedtowards the target.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further features and advantages of the invention will becomeapparent to the skilled reader from the following description ofpreferred embodiments made with reference to the accompanying Figures inwhich:

[0020]FIG. 1 is a partial cross-sectional elevation of the ion sourceaccording to the invention,

[0021]FIG. 2 is a plan view of the ion sources in FIG. 1,

[0022]FIG. 3 shows an example of a cathode filament waveform signal,

[0023]FIG. 4 is a side view of a gas delivery system with a genericcontrol valve adjacent the outlet,

[0024]FIG. 5 is shows an example of an outlet control valve, and

[0025]FIG. 6 is a schematic of an ion source combined with IADdeposition apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] In a typical ion source electrons are drawn from a cathodefilament toward an anode through an ionisable gas. Collisions betweenthe gas molecules and energetic electrons create a source of positiveions by inducing a plasma. In one type of ion source known as a gridlession source, a magnetic field is applied across the plasma to shape theions accelerated from the ion source into an ion beam. In a specifictype of gridless ion source, known as an end-Hall effect ions the axisof the magnetic field is aligned with the electric potential between thecathode and the anode. The interaction of the magnetic and electricfields causes the charged particles to approximately follow the magneticfield lines. The anode in these devices is typically annular having anoutwardly inclined inner diameter with the bulk of the plasma formingwithin the confines of the anode walls.

[0027] A specific ion source is described below but it is to beunderstood that the description is for illustrative purposes only. Thepresent invention can be suitably adapted for use with any one ofseveral known ion sources.

[0028]FIGS. 1 and 2 show an ion source generally at 10 having a cathodewire 11 and an anode 12. The anode 12 is an annulus having an innersurface 35 sloping outwards in the direction of the cathode. Between thecathode 11 and the anode 12 is an ionisation region 13. The cathode wire11 is suspended above the anode by two mounting pins 20 that are heldby, and in electric isolation from a shield plate 30. The shield plate30 substantially surrounds the anode, cathode and ionisation region byextending from a point lower than the anode 12 to a point above thecathode 11 and is preferably maintained at earth potential to shield theanode and the cathode from external fields. A magnet 14 is disposedoutside the ionisation region 13 but adjacent the anode 12. The magnet14 creates a magnetic field, the longitudinal axis of which is alignedwith the axis of the anode 12. The magnet may be a permanent magnet oran electromagnet. Preferably the magnet is a high flux rare earth magnetsuch as a NdFeB magnet. As an alternative, magnet 14 may be a ringmagnet disposed around the anode 12 and ionisation region 13.

[0029] The alignment of the magnetic field with the electric fieldcauses electrons emitted by the cathode to approximately follow themagnetic field lines as they move towards the anode. This has the effectof concentrating the flow of electrons toward the axis of the magneticfield. Therefore the reason where the magnetic field intensity is amaximum, will also be a region of maximum electron flux.

[0030] The ionisable gas, for example oxygen, nitrogen or argon, issupplied to the ion region through a gas flow path from gas feed line22. The gas flow path terminates at an outlet member 15. The outletmember 15 has the form of a gas shower head, with a plurality ofapertures 17, that introduce the gas into the ionisation region 13 in asubstantially random direction. The gas shower head 15 is disposed onthe axis of the anode and adjacent the ionisation region 13 such thatgas emanating from the apertures 17 enters the ionisation region at apoint of high electron flux. Because a large proportion of ionisationoccurs is close to the outlet the gas shower head is of a material suchas stainless steel, that withstands the very high energy from theincoming electron flux.

[0031] The anode 12 preferably has disposed within it a channel 53 incommunication with a fluid conduit 55 that provides water to cool theanode. The channel 53 preferably extends into the body of the outletmember 15.

[0032] The anode 12, outlet member 15 and shield 30 are mounted on a nonconductive mounting base 50 through which extends the gas flow path andfluid conduit 55. A plurality of mounting screws 57 fix the anode 12 tothe base 50. The magnet 14 is housed within the base such that theexternal pole is exposed. The mounting base 50 has a conduit 58 thatforms part of the gas flow path and connects the gas feed line 22 to theoutlet member 15 such that no electrical connection can be made betweenthe outlet member 5 and the gas feed line 22. The mounting base 50 has asimilar conduit for connecting the water feed line 55 to the channel 53.The gas and water feed lines preferably screw into the mounting base 50.A suitable material for the mounting base 50 is glass filledpolytetrafluoroethylene. This arrangement reduces electrical hazards,simplifies mounting and installation and reduces risk of secondaryplasmas forming within the gas feed line.

[0033] The size of the outlet is preferably half or less than thesmallest inner diameter of the anode in order that a localised highpressure zone is created around the outlet, that decreases rapidly withdistance.

[0034] In operation the anode is charged in the range 0-500 V,preferably 250 V relative to the cathode which is at or near earthpotential. A DC current of approximately 12A is passed through thecathode to stimulate electron emission. An AC current may be used butthe combination of an alternating current and the magnetic field hasbeen found by the present inventor to cause vibrations in the cathodewhich reduces the cathode lifetime. Electrons generated at the cathodeare influenced by the anode potential and are accelerated toward it. Themagnetic field imparts a spiral motion on the electrons furtherincreasing their kinetic energy and thus their potential to ionise gasmolecules, and focusing the electrons toward the longitudinal axis.Collisions between the energetic electrons with gas molecules emittedfrom the outlet member 15 cause ionisation. If sufficient ionisingcollisions occur then a plasma is formed. Positive ions created if theplasma experience the opposite effect to the electrons. The ionsinitially have a random velocity but are influenced by the electricpotential gradient which accelerates them toward and past the cathode11. The magnetic field in this case acts to control the direction inwhich the ions are expelled from the ion source by focusing them into anion beam or ion current centered on the longitudinal axis of themagnetic field. By properly aligning the axis of the magnetic field, theion beam can be directed toward a target. Further features of the abovedescribed ion source can be obtained from the present applicant'sco-pending application no. PCT/AU99/00591, the contents of which areincorporated herein by reference.

[0035] In a first embodiment, the cathode filament 11 is connected to aDC power supply that incorporates a variable waveform signal generator.The cathode filament has a DC biased current of 8-9 A which is a least70% and preferably 75-95% of the threshold current required forthermionic emission (shown in broken line in FIG. 3). This current issupplied to the filament as a continuous wave (CW) signal (FIG. 3a).Superimposed on the base signal is a square pulse signal of approx 3 A.(FIG. 3b) The combined signal (FIG. 3c) is sufficient to producethermionic emission during peak periods of the supplementary pulsesignal. Because electron emission from the cathode, and subsequently gasionisation, only occurs when there is sufficient cathode current, theion source will only produce an ion current during peak times of thecathode current cycle. When the pulse signal finishes and the totalfilament current returns to the base level there is no thermionicelectron emission to excite ionisation of the gas and this the ion beamcurrent falls to zero.

[0036] The of the basic filament signal and the pulse signal can bevaried by the signal generator depending upon requirements and the typeof cathode filament employed, as can the duty cycle and frequency of thepulse signal.

[0037] The present inventor has found it suitable to bombard the targetwith ions for between 0.5 and 5 seconds, preferably 1 second, for every5 to 30 nm, preferably 10-20 nm of deposition, which correspondsapproximately to having a cathode filament pulse signal period of approx5 to 50 seconds, preferably 10 seconds, with duty cycle of 5% to 30%preferably 10%. With these parameters, the ion beam current grows anddecays on a time scale much shorter than the length of time for whichthe ion beam current is on during each cycle.

[0038] By providing the filament with a CW base current to which isadded a periodic pulse current, as opposed to providing one pulse signalof greater amplitude, thermal shock of the filament is prevented therebyincreasing filament lifetime.

[0039] An alternative embodiment for producing an intermittent ion beamcurrent is described with reference to FIG. 4. In this embodiment, it isthe flow of gas into the ionisation region that is cyclic. FIG. 4 showsa gas outlet 15 that is disposed adjacent the ionisation region of theion source. The outlet is supplied with gas through a gas feed line 22.

[0040] An electrically controlled valve 43 within the gas flow path 22is provided with a signal from the signal generator 45 to control itsopening and closing thereby governing the flow of gas into theionisation region 13.

[0041] The waveform used to control the operation of the valve can bethe same square pulse wave used in the cathode filament embodimentdiscussed above. However, the rise time of the ion beam cart and titsubsequent decay will be longer than for the embodiment of the cyclicfilament current discussed above due to the lag in gas entering theionisation region once the valve 43 is open and residual diffusion ofgas from the gas path downstream of the valve 43 once the valve isclosed Therefore the pulse which is used to keep the control of valve 43open may need to be slightly longer than the analogous filament currentpulse in order to provide the same effective ion beam current intensityand duration. It is also important that the valve 43 be placed as closeto the outlet as possible to reduce the amount of residual gas in thefeed line downstream of the valve once the valve is closed.

[0042] One proposed embodiment for the valve is discussed with referenceto FIG. 5 in which a solenoid coil 60 is wrapped a the gas feed line 22.An amaze 61 disposed within the gas line 22 in a first position engagesa valve seat 63 to close the valve and in a second position allows gasto flow through the line to the outlet The armature 61 is ferromagneticand/or paramagnetic and in normal conditions will be biased, either by aspring 65 or by the magnetic field of the rare earth magnet 14 used forcontrolling expulsion of ions from the plasma to close the valve. Achange in the electric current in the solenoid 60 as governed by thewaveform from the signal generator 45 creates a change in the localmagnetic conditions around the armature 61. This has the effect ofdrawing the armature 61 away from the valve seat 63 thereby allowing gasflow A reverse change in the charging state of the solenoid causes thearmature 61 to re-engage the valve seat 63.

[0043] It is preferred that the armature 61 be magnetised such that inthe absence of the solenoid field, the armature 61 is repelled by therare earth magnet 14 to the closed position. When the solenoid ischarged the solenoid field overcomes the field from the magnet 14 andacts to open the valve. In this way, the gas line remains closed in theabsence of any power.

[0044] In an alternate system, the valve may be a piezo-valve opened andclosed as the governing signal from the waveform generator goes betweenhigh and low values.

[0045] In a further embodiment one or more gas injectors can be used inplace of the gas outlet and valve The gas injectors inject a measuredvolume of gas into the ionisation region. The timing of the gasinjection can be controlled by the waveform generator.

[0046] An advantage of periodic or cyclic gas flow is that the overallamount of gas provided to the ionisation region can be reduced becauseno gas is provided during times when no ion current is required, andthus smaller and/or cheaper vacuum pumps can be used to achieve the lowpressures required for optimum IAD conditions.

[0047] A more significant advantage is that with pulsed gas flow it ispossible to achieve higher localised gas pressures in the ionisationregion whilst still maintaining a low background pressure for the samepump system. This is because the average gas flow and thus the averagebackground pressure over a number of cycles is lower for pulsed gas flowthan for continuous gas flow conditions using the same gas flow rates.The system can thus tolerate higher gas flow rates during the on-phaseof the gas flow cycle without introducing instabilities into the systemthat are caused by high background pressures. The higher gas flows,create higher ionisation region pressures giving rise to higher ion beamcurrents.

[0048] A further method for creating a pulsed ion beam current is toprovide the ion source anode 12 with a square pulse waveform voltageranging from 0 V to its normal operating voltage eg 250 V, relative tothe cathode. When the anode voltage is high, the ion source operates asnormal to produce an ion beam current When the anode voltage goes low,electrons create at the cathode are not influenced by the anode voltageand thus do not preferentially accelerate toward the ionisation region.Thus minimal excitation collisions occur and no meaningful ion beam isproduced.

[0049] Further methods for producing a cyclic ion beam may be possible.For example, in ion sources where an electromagnet is used to shape anddirect the ion beam, the electromagnet may receive a pulsed signal sothat the directional effects that cause the ions to flow toward thetarget are produced only intermittently.

[0050] It is of course possible to combine any of the above describedmethods to produce a intermittent ion beam current.

[0051] Referring to FIG. 6 there is schematically shown an ion assistedthin film deposition system including an ion source 70 according to theinvention, deposition apparatus 71 and a target substrate 72 alldisposed within a vacuum chamber 73. The power supply 74 operating theion source includes a waveform generator 45 used to produce a periodicion beam 80 directed toward the target substrate 72. The depositionapparatus 71 produces the vapour stream of material 79 to be depositedand may employ any known technique used in physical vapour deposition,such as thermal evaporation or electron beam evaporation. The specificvaporisation techniques used will depend on the type of material beingdeposited mid the substrate type.

[0052] In operation, a pre-determined thickness of material isdeposited, without ion assistance, which results in the growth of astoichiometric deposit with low pacing density. The deposited film isthen bombarded with a short-duration high-energy pulse of ions. Thisprocedure is repeated until the full thickness of film is achieved. Theresult is a strongly adherent, stoichiometric film with good bulkdensity and optical properties.

[0053] In a most preferred form of the invention, deposition of thecoating material onto the target 72 also occurs cyclically with each ofthe stages of deposition and ion bombardment occurring non-concurrently,that is, to the exclusion of the other stage. The waveform generator 45can be used to control the vaporisation apparatus 71 with a signal thetemporal inverse of the signal used to control the ion source. Thetarget 72 thus receives a repeated cycle consisting of exclusive anddistinct deposition and ion bombardment stages.

[0054] In an alternative foe, the vaporisation apparatus may have ashutter member 78 that is actuated at the start of the ion bombardmentphase of the total process cycle to block the stream of depositionmaterial 79 to the substrate so that further deposition material isprevented from reaching the target whilst ion bombardment is The shuttercan be controlled by the same waveform from the waveform generator thatcontrols the ion source. On completion of the ion bombardment phase theshutter is moved out of the stream of deposition material.

[0055] Instead of using the waveform generator to trigger production ofthe ion beam current, the jolt source may use an external trigger. Forexample, the ion source may receive feedback from a deposition monitor76, e.g. a quartz crystal monitor, that measures growth of the depositedfilm in situ. Once a predetermined thickness of film has been depositeda control signal may be generated to trigger the ion source to provide apulse of ions causing densification of the most recently deposited film.The pulse size and random may still be governed by the waveformgenerator or by other means. The same trigger used to advocate the ionbeam may control the vaporisation apparatus and/or shutter member toprevent further film material from being deposited on the substrateduring ion bombardment.

[0056] The duration of the ion bombardment phase is predetermined by thepulse length setting on the waveform generator.

[0057] At the conclusion of the ion bombardment phase, the pressure maybe higher than is required or desirable for the deposition phase due tothe injection of gas into the ion source. A pressure transducer 75disposed within the vacuum chamber can measure the chamber pressurewhich the system can use to prevent the deposition process fromrecommencing until the pressure is below a pre-determined level.

Case Study 1: Magnesium fluoride

[0058] Magnesium fluoride is a very commonly used thin film material forapplication to both single and multi-layer antireflection coatings. Itpossesses a low refractive index (n=1.35 at 550 nm) and a transparencyrange or the deep ultraviolet to the far infrared. Conventionaldeposition requires high substrate temperatures (=300° C.) which canincrease processing time in multi-stage processes and considerably,increase the risk of damaging thermally sensitive substrates.Comparative results for deposition of magnesium fluoride with continuousand periodic ion bombardment of the target are shown in Table 1 below.TABLE 1 Method of Deposition Properties n @ 550 nm Evaporated-unheatedSoft, easily damaged 1.35 substrates low packing density; high stress,unstable Evaporated- More durable, 1.39 typical hot 300° C. n increasingIAD O+, cold Dense, n increasing 1.40-1.43 IAD Ar+, cold Dense, kincreasing 1.40 PULSED O+ IAD* Very durable, 1.35 (bulk) Unheatedsubstrates High transparency

Case Study 2. Calcium Fluoride

[0059] Bulk calcium fluoride possesses the lowest refractive index ofany thin film material with an index of n=1.21 (bulk) at 550 nm. Thematerial has a very wide transparency range comparable to magnesiumfluoride above. Evaporated CaF₂ thin films have a packaging density ofonly 50%-60% and are thus extremely soft and easily damaged, making italmost essential that they are used in a clean environment as wipingwill quickly damage the coating. Table 2 shows comparative data forcalcium fluoride films deposited with and without pulsed ionbombardment. TABLE 2 Method of Deposition Properties n @ 550 nmThermally Very fragile and =1.20 in vacuum evaporated-cold unstable,large vacuum =1.28-1.30 in air to air shift, uncleanable. PULSED-O+ IAD*Soft but stable films =1.22 to 1.23 Unheated substrates negligiblevacuum to air shift. Cleanable.

[0060] Because the ion source of the present invention operates in acyclic mode so that the ion beam is only produced for brief periods,instabilities that grow within the ion source during the on-phase maynot be fatal to the ion source's operation if the ion source switches tothe off phase before a catastrophic event, such as the development of avacuum arc, occurs. For example, it may be possible to have a higher gasflow rate during the on-phase of a pulsed ion beam system than for acontinuous system, giving rise to a higher ion beam current, because bythe time the pressure outside the ionisation region reaches the levelswhere vacuum arcs may occur, the waveform signal will go low thusswitching off the gas flow. The potential instability will thenstabilise before the next on-phase of the cycle commences.

[0061] Using an intermittent ion beam in ion assisted deposition offilms prevents or at least reduces the problems discussed above of priorart IAD systems such as ion species depletion and displacement. This isbecause minimal new material is deposited during the ion bombardmentphase of the cycle. Thus the ion beam serves only as a source of energyfor densifying the already deposited material. The problems of the priorart can be further reduced by excluding deposition totally during theion bombardment phase.

[0062] The present invention has further enabled the production ofstable, optical quality UV films.

[0063] While particular embodiments of this invention have beendescribed, it will be evident to those skilled in the art that thepresent invention may be embodied in other specific forms withoutdeparting from the essential characteristics thereof The presentembodiments and examples are therefore to be considered in all respectsas illustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than foregoing description, andall changes which come within the meaning and range of equivalency ofthe claims are therefore intended to be embraced therein It will furtherbe understood that any reference herein to known prior art does not,unless the contrary indication appears, constitute an admission thatsuch prior art is commonly known by those skilled in the art to whichthe invention relates.

I claim:
 1. An ion source including: an ionisation region; a gas supply;a gas excitation system: ion influencing means; and an ion sourcecontroller, wherein said gas supply supplies an ionisable gas to saidionisation region; wherein said gas excitation system causes ionisationof gas in said ionisation region; wherein said ion influencing meansforms ions produced in said ionisation region into an ion currentbstantially directed at a target, and wherein said ion source controllercontrols said ion source so as to intermittently produce said ioncurrent.
 2. An ion source according to claim 1 wherein said ion sourcecontroller includes a signal generator producing a regular waveformsignal controlling the production of said ion current.
 3. An ion sourceaccording to claim 1 wherein the commencement of said ion current is inresponse to an external trigger received by said ion source controller,said ion source controller further including a timer for controlling theduration of said ion current
 4. An ion source including: an ionisationregion a gas supply; a cathode; a cathode emission controller, an anodean electric potential generator; and ion influencing means; wherein saidgas supply supplies an ionisable gas to said ionisation region; whereinsaid cathode is disposed at one end of said ionisation region; whereinsaid anode is disposed at an opposite longitudinal end of sad ionisationregion; wherein said cathode emission controller causes said cathode toemit electrons; wherein said electric potential generator generates aelectric potential between said cathode and said anode; wherein saidgenerated electric potential causes electrons emitted by said cathode toaccelerate in the direction of said anode; wherein electrons movingtoward said anode bombard said ionisable gas to produce ions; whereinsaid ion influencing means forms ions produced in said ionisation regioninto an ion current substantially directed at a target; and wherein saidcathode emission controller causes intermittent emission of electronsfrom said cathode such that said ion source produces an intermittent ioncurrent.
 5. An ion source according to claim 4 wherein said cathodeemission controller generates a waveform current signal that is providedto said cathode to stimulate emission of electron from said cathode. 6.An ion source according to claim 4 wherein said cathode emissioncontroller generates a DC current signal that is provided to saidcathode to stimulate emission of electrons font said cathode, whereinsaid DC current signal includes a continuous base current signal below athreshold current required for election emission from said cathode andan intermittent pulse current signal superimposed on said base currentsignal and wherein the combination of said base current and said pulsecurrent is above the threshold current required fix electron emissionfrom said cathode.
 7. An ion source according to claim 6 wherein thepulse current signal has a duty cycle between 5% and 20%.
 8. An ionsource according to claim 6 wherein the total current to said cathode isabove the threshold for electron n for 5 to 20% of the total signalperiod.
 9. An ion source including: an ionisation region; a gas supply;a gas excitation system; ion influencing means; and a gas flowcontroller; wherein said gas supply supplies an ionisable gas to saidionisation region; wherein said gas excitation system causes ionisationof gas in said ionisation region; wherein said ion influencing meansforms ions produced in said ionisation region into an ion currentsubstantially directed at a target and wherein said gas flow controllercontrols the flow of gas into said ionisation region so as tointermittently produce said ion current.
 10. An ion source according toclaim 9 wherein said gas supply includes a gas line, an outlet in saidgas line to said ionisation region and a valve disposed in said gas lineto control the flow of gas to said outlet wherein said gas flowcontroller includes a signal generator and wherein said signal generatorgenerates a signal to control the opening and closing of said valve. 11.An ion source according to claim 10 wherein said valve is substantiallyadjacent said outlet.
 12. An ion source according at claim 10 whereinsaid signal is a regular pulse waveform signal.
 13. An ion source accordto claim 12 wherein said regular pulse waveform signal has a duty cycleof between 5% and 30%.
 14. An ion source according to claim 10 whereinsaid valve is electrically controlled by a signal from said signalgenerator.
 15. An ion source according to claim 10 wherein said valveincludes a valve seat formed in said gas line, an armature disposed insaid gas line, and a coil disposed around said gas line, wherein saidarmature is adopted to sealing engage said valve seat to prevent theflow of gas through said gas line, wherein said coil is charged by asignal from ad signal generator, and wherein said armature disengagessaid valve seat in response to a change in the charging state of saidcoil.
 16. An ion source according to claim 15 wherein said armature isbiased towards a position in which said armature engages said valveseat.
 17. An ion source according to claim 16 further including a magnetwherein the magnetic field from said magnet biases said armature toengage said valve seat.
 18. An ion source according to claim 9 whereinsaid gas supply includes one or more gas injectors, wherein said gasinjectors inject a measured amount of gas into said ionisation regionmid wherein the injection of gas from said gas injectors is controlledby said gas flow controller.
 19. An ion source including: an ionisationregion a gas supply; a cathode; a cathode emission controller, an anodean electric potential generator, and ion influencing means; wherein saidgas supply supplies an ionisable gas to said ionisation region; whereinsaid cathode is disposed at one end of said ionisation region; whereinsad anode is disposed at an opposite longitudinal end of said ionisationregion; wherein said cathode emission controller causes said cathode toemit electrons; wherein said electric potential generator generates anelectric potential between said cathode and said anode; wherein saidgenerated electric potential causes electrons emitted by said cathode toaccelerate in the direction of said anode; wherein electrons movingtoward said anode bombard said ionisable gas to produce ions; whereinsaid ion influencing means forms ions produced in said isation regioninto an ion current substantially directed at a target; and wherein saidelectric potential is generated ionisation such that said ion sourceproduces an intermittent ion current.
 20. An ion source according toclaim 19 wherein said electric potential generator provides an electricpotential to said anode that causes electrons emitted by said cathode toaccelerate in the direction of said anode.
 21. A thin film depositionsystem including deposition apparatus and an ion source according toclaim 1 wherein said deposition apparatus ejects a stream of depositionmaterial toward said target.
 22. A thin film deposition systemincluding: deposition apparatus; an ion source; an ion sourcecontroller; and at least one target substrate; wherein said depositionapparatus ejects a steam of deposition material towards said target,wherein said ion source creates an ion current substantially directed atsaid target substrate, wherein said ions source controller controls saidion source so as to intermittently produce said ion current, and whereindeposition of material onto said target substrate is substantiallyprevented whilst said target substrate is subjected to said ion current.23. A system according to claim 22 further including a shutter memberthat substantially blocks said stream of deposition material whilst saidtarget substrate is subjected to an ion current.
 24. A system accordingto claim 23 wherein said shutter member is controlled by said ion sourcecontroller.
 25. A system according to claim 24 wherein said ion sourcecontroller includes a signal generator producing a pulse waveform signalthat controls said ion source and said shutter member.
 26. A systemaccording to claim 22 further including a pressure monitor wherein saidpressure monitor measures the pressure of said system and whereindeposition of material onto said target substrate recommences inresponse to a pressure measurement below a predetermined level.
 27. Athin film deposition system including: deposition apparatus; an ionsource; an ion source controller, at least one target substrate; and adeposition monitor; wherein said deposition apparatus ejects a stream ofmaterial toward said target, wherein said ion source creates an ioncurrent substantially directed at said target substrate, wherein saidion source controller controls said ion source to produce said ioncurrent for a predetermined duration, wherein said deposition monitormonitors the increase in thickness of material deposited on said targetsubstrate, and wherein said deposition monitor triggers said ion sourceto commence production of said ion current in response to a measuredincrease in deposited material above a predetermined level.
 28. A systemaccording to claim 27 wherein said predetermined level is between 5 and30 mn.
 29. A system according to claim 27 wherein said predeterminedduration is between 0.5 and 5 seconds.
 30. A control system forcontrolling an ion-assisted deposition process including : a depositionmonitor a pressure monitor; an ion source controller; and a depositioncontroller; wherein said deposition monitor monitors the increase inthickness of deposition material on a substrate, wherein said pressuremonitor measures the pressure within a vacuum chamber in which said ionassisted deposition process occurs, wherein a first control signal isgenerated in response to a measurement by said deposition monitor of anincrease in thickness of deposited material on said substrate above apredetermined amount, wherein said deposition controller causesdeposition of material onto said substrate to cease in response to saidfirst control signal, wherein said ion source controller causes an ionsource to produce an ion current directed at said substrate for apre-determined duration in response to said first control signal,wherein after the expiration of said predetermined duration a secondcontrol signal is generated in response to a measurement of pressure bysaid pressure monitor below a predetermined pressure, and wherein saiddeposition controller causes the deposition of material on saidsubstrate to recommence in response to said second control signal.